Melanoma is a malignant tumor developing by transformation of melanocytes, the cells which produce the pigment melanin that colors skin, hair, and eyes and is heavily concentrated in most moles. The majority of melanomas, therefore, are black or brown. However, melanomas occasionally stop producing pigment. When that happens, the melanomas may no longer be dark, but are skin-colored, pink, red or purple.
Melanoma is the most serious form of skin cancer. Its incidence and mortality rates in fair-skinned populations increase worldwide. While it is not the most common of the skin cancers, it causes the most deaths. The American Cancer Society estimates that in 2007, there will be around 60 000 new cases of melanoma in the United States.
Everyone is susceptible to develop a melanoma, but depending on several factors, the risk can be increased, inter alia sun exposure, number of moles on the skin, skin type and genetic background. Indeed, both UVA and UVB rays can induce skin cancer, including melanoma. The presence of the two types of moles, normal moles and atypical moles, known as dysplastic naevi, are indicative of an increased risk of melanoma. Regarding the genetic predisposition, it is known that about 10% of the patients diagnosed with melanoma have a family member with a history of melanoma.
Primary melanomas are likely to produce metastases, indicative of the spread of cancer from its primary site to other places in the body. Cancer cells can break away from a primary tumor, penetrate into lymphatic and blood vessels, circulate through the bloodstream, and grow in a distant focus (metastasize) in normal tissues elsewhere in the body.
Presence of metastases carries a severe prognosis due to ineffective response to treatments. Regarding diagnosis, moles that are irregular in color or shape are suspicious of a malignant or a premalignant melanoma. Following a visual examination and a dermatologic exam, a biopsy of the suspicious mole may also be made. If it is malignant, the mole and an area around it need excision to avoid expansion and spread.
Clinical and histopathological criteria are useful as indicators for patients presenting primary melanoma. However it is widely admitted that precise diagnostic and prognostic markers would be beneficial for a number of patients.
Early and reliable diagnosis of a melanoma is thus of outmost importance.
Melanomas are also frequently observed on horses, where they are the most common skin tumors in adult horses. Melanomas have been shown to occur more commonly in Arabian, Lipizzaner, and Percheron breeds, as these breeds have a high incidence of gray horses and melanomas are mostly found in gray horses. These melanomas are generally found around the lips, eyes, ears, salivary glands, anus, penis, and vulva. Most melanomas in gray horses are benign slow-growing tumors that rarely metastasize or spread to other organs. However, the tumor can spread to other organs, especially in non-gray horses. Generally, these tumors do not cause a problem other than with urination, defecation, or breeding. However, they can invade local tissue and can cause lameness as well as neurological problems by invading the central nervous system.
Melanomas can also be observed on dogs. Although found primarily on the skin, in the dog, they can also be found in the oral cavity. Early diagnosis of melanomas can lead to more successful attempts at removal and identification of the grade or stage of cancer. Even the benign forms of cutaneous tumors can be locally invasive. Melanomas can metastasize (spread) to any area of the body especially the lymph nodes and lungs and present very challenging and dangerous prospects for the dog. Cats are also susceptible to melanoma tumors, however in a lesser extent than dogs.
Diagnosis of melanoma is thus also problematic from a veterinary point of view.
The diagnosis of melanoma requires experience, as early stages may look identical to harmless moles or not have any color at all.
If a melanoma is recognized and treated early, it is nearly 100 percent curable. But if it is not, the cancer can advance and spread to other parts of the body, where it becomes hard to treat and can be fatal.
There is thus a need for new tools allowing early and reliable diagnosis of melanoma.
Moreover, understanding the molecular bases of melanoma progression could help developing more effective treatments. Mechanisms of melanocyte transformation are thus widely studied.